---
title: "Short note: Datagram network"
subject: "Telecommunications"
chapter: 8
key: "semester_8/telecommunications:short-note-datagram-network"
source: https://www.bctengineer.com/q/semester_8/telecommunications/short-note-datagram-network
site: BCT Engineering
---

# Short note: Datagram network

Telecommunications · Chapter 8: Data Communication

- Asked in: 2081 Chaitra, 4 marks; 2081 Bhadra, 4 marks; 2080 Bhadra, 4 marks (asked 3 times)
- Video: [Datagram Networks](https://www.youtube.com/watch?v=n1f0iGNVGps) — TutorialsPoint
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/telecommunications/short-note-datagram-network
- Whole chapter: https://www.bctengineer.com/md/semester_8/telecommunications/chapter-8

## Question

Write a short note on datagram network.

## Short answer

A datagram network routes each packet independently with full addresses, without connection setup. Packets may follow different paths and arrive out of order. It is robust and efficient but has variable delay and no guaranteed QoS; the Internet uses this model.

## Answer

A **datagram network** is a packet-switched network in which each packet (**datagram**) is treated **independently**; there is no connection setup. Every packet carries the full source and destination address, and each router decides the route for it separately using its routing table. The internet (IP) is a datagram network.

```text
       +--R2--+
 A ----R1     R4---- B
       +--R3--+
 packets 1,3 via R2; packet 2 via R3
 B may receive 1,3,2 (reordering)
```

**Features**

- Connectionless: no setup or teardown phase.
- Each packet may follow a different path.
- Packets may arrive **out of order**, be duplicated or lost; higher layers (e.g. TCP) fix this.
- Routers keep no per-connection state; routing tables depend only on the destination address.
- Resources are not reserved, so delay varies.

**Advantages**

- No setup delay; good for short, bursty traffic.
- Robust: if a router or link fails, packets are routed around it.
- Efficient use of links.

**Disadvantages**

- Larger header (full address) in every packet.
- Variable delay, reordering, no guaranteed QoS.

| Point | Datagram | Virtual circuit |
|---|---|---|
| Setup | none | needed |
| Addressing | full address | short VC number |
| Route | per packet | fixed per call |
| Order | not guaranteed | in order |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How is each packet treated in a datagram network?
   A. Independently, with no connection setup
   B. Along a path fixed at setup
   C. After reserving resources
   D. Using a short VC number
   Answer: A. Each datagram is routed independently by routers from its full destination address. (Key point: Datagram principle)

2. Why may packets arrive out of order in a datagram network?
   A. Routers drop the oldest packets
   B. Packets may follow different paths
   C. Headers are too short
   D. TCP forbids ordering
   Answer: B. Packets may take different paths, so higher layers like TCP fix ordering. (Key point: Out-of-order delivery)

3. Which is a disadvantage of datagrams compared with virtual circuits?
   A. Setup delay
   B. Packets can't route around failures
   C. Each packet carries the full address, giving a larger header
   D. Per-connection state in routers
   Answer: C. Full address in every packet, variable delay and no guaranteed QoS are disadvantages. (Key point: Header overhead)

4. Why is a datagram network robust?
   A. Routes are fixed per call
   B. Resources are reserved
   C. Routers keep per-connection state
   D. If a router or link fails, packets are routed around it
   Answer: D. No fixed path exists, so packets can be rerouted. (Key point: Robustness)